Whereas I'd put money on "John's a rookey ookey" being a phonetic rendering of something that made sense in... um... a different language. No idea what, though.

I wonder if "John Kanakanaka" and "John Cherokee" were even references to a person. If there were a word meaning "haul" or "hold" or "let's get going" that sounded a bit like "john"... Wildly speculative, I'm afraid.

Interesting question!